1. Field of the Invention
The present invention relates to an antenna duplexer and, more particularly, to an antenna duplexer constructed of a combination of antenna duplexers which include surface acoustic wave (SAW) filters used for mobile communication devices.
2. Description of the Related Art
With recent development of mobile communication systems, mobile phones, portable communication terminals and other mobile communication devices have been rapidly coming into widespread use. Because these devices are desired to be smaller in size and more powerful in performance, components used in these devices are also required to be reduced in size and improved in performance.
As regards mobile phones, two kinds of radio communication systems, i.e., digital and analog, are employed, and a diversity of frequencies in a 800 MHz to 1 GHz band and a 1.5 GHz to 2.0 GHz band are used for radio communications.
In mobile communication devices, antenna duplexers are used as components in RF sections which branch and generate signals transmitted and received through antennae.
FIG. 30 is a block diagram illustrating the construction of a high frequency part of a conventionally used mobile phone.
Audio signals 100 input from a microphone are modulated into modulated signals by a modulator 101 according to a modulation system of the mobile phone, and further converted to a designated carrier frequency by a local oscillator 108. Thereafter the converted audio signals pass through an interstage filter 102 for selecting signals of the designated transmitting frequency alone, are amplified to a desired signal amplitude by a power amplifier 103 and sent to an antenna duplexer 105. The antenna duplexer sends signals of the designated transmitting frequency alone to an antenna 104, from which the signals are transmitted into the air as radio signals.
On the other hand, signals received by the antenna 104 are sent to the antenna duplexer 105, where only signals of a designated frequency are selected. The selected signals are amplified by a low-noise amplifier 106 and passed through an interstage filter 107. Only speech signals are selected by an IF filter and taken out as audio signals 100 by a demodulator 111. The antenna duplexer 105 is located between the antenna 104 and what is called an audio signal processing circuit, and has the functions of distributing transmitted and received signals and avoiding their interference.
Further, for responding to diversification of radio communication systems, dual-mode and dual-band techniques are employed for imparting higher-levels of functions to mobile phones.
The dual-mode technique means, for example, a technique for providing a single mobile phone with analog/digital compatibility or TDMA (time-division multiplexing access)/CDMA (code-division multiplexing access) compatibility in digital communications.
The dual-band technique means a technique for providing a single mobile phone with access to two bands, for example, 800 MHz band and 1.9 GHz band, or 900 MHz band and 1.8 GHz band (or 1.5 GHz band).
For supporting such high-levels of functions of mobile phones, it is demanded that filters used for mobile phones also have a dual-port or dual-band function (hereinafter the phase xe2x80x9chave a dual functionxe2x80x9d is used for indicating having either function). As filters having a dual function, filters having two inputs and two outputs and filters having one input and two outputs have been developed. As regards the one-input two-output filters, a phase matching circuits is usually added outside the filters because terminals on a commonized side must be gathered together.
In the case of filters used between stages in the RF section for branching and generating signals from/to the antenna, an IF section and other sections (so-called interstage filters), combinations of transmitting filters alone and combinations of receiving filters alone are put to practical use as dual-function filters.
For providing the dual-band access to antenna duplexers, antenna duplexers have been developed which uses dielectric duplexers for branching and generating signals of least one pass band.
FIG. 27 shows the construction of a dual-function antenna duplexer D3 which is composed of a duplexer D1 for branching and generating signals of a higher pass band frequency and a duplexer D2 for branching and generating signals of a lower pass band frequency.
Here, PA denotes a power amplifier, LNA denotes a low-noise amplifier, and SW1, SW2 and SW3 denote circuit changing switches. The duplexers D1 and D2 are each composed of a transmitting filter (T1 or T2), a receiving filter (R1 or R2) and a phase matching circuit (L1 or L2).
In the North American PCS system and the European DCS1800 system which require a narrow frequency band gap (or transition band) between transmitting and receiving pass band frequencies, if dielectric duplexers are used, the size of the duplexers themselves becomes as large as about 2.8 cmxc3x970.9 cmxc3x970.5 cm, which prevents reduction in size and in thickness of portable terminal devices.
Also antenna duplexers have been developed in which SAW filters are used for the transmitting filters (T1, T2) and the receiving filters (R1, R2) shown in FIG. 27.
As such duplexers constructed with use of SAW filters, proposed are module-type duplexers in which two SAW filters and matching circuits are packaged on printed circuit boards and one-piece duplexers in which two SAW filters of a bare type are mounted in multi-layered ceramic packages and matching circuits are mounted within the packages. Such SAW filters can be reduced in size and thickness to a volume of about one-third to about one-fifth of that of dielectric filters and to a thickness of about half to about one-third of that of the dielectric filters.
In FIG. 27, one duplexer D1 has three terminals ANT1, Tx1, Rx1 and grounding terminals, not shown. These terminals and external terminals (SW1, SW2, SW3, PA, etc.) are connected to a filter chip via terminals provided to the package by wire bonding or the like.
One duplexer as shown in FIG. 27 is a so-called three-port device having three terminals ANT1, Tx1 and Rx1. In the antenna duplexer D3 having two of such duplexers in combination, it is difficult to construct circuits so as to separate a transmitting circuit (Tx1, Tx2, SW2 and PA), a receiving circuit (Rx1, Rx2, SW3, LNA) and an antenna circuit (SW1, ANT2, ANT2) from the viewpoint of connection to external circuits.
In other words, an inappropriate arrangement of the connecting terminals such as Tx1, Rx1 and the like may lead to crossing of connecting wires, which results in interference of signals and/or generation of noises. Consequently, desired filter characteristics may not be obtained.
A well-designed wiring on printed circuit boards for mounting filter chips may enable the separation of the above-mentioned three circuits to some extent. However, at the stage of designing circuit boards, it is extremely difficult to decide patterns and layouts for the circuits with considering interference between signals and required specifications of a small-sized dual-function antenna duplexer.
Therefore, for responding to demand for dual function and size reduction, it is necessary to contrive a clever arrangement of connecting terminals on the package of the antenna duplexer D3 containing the two duplexers D1 and D2.
As regards SAW filters used for the transmitting filter T1 and the receiving filter R1 of the duplexer, in general, size reduction is considered to be possible if an increased number of filter chips are mounted in one filter package or if an increased number of SAW filters are formed on one filter chip.
However, even if a large number of SAW filters are formed on each of filter chips which are then made into two pairs of transmitting filters and receiving filters, further idea is still necessary for avoiding interference between the filter characteristics of the transmitting filters and the receiving filters when an antenna duplexer is constructed of the filters. For this purpose, a phase matching circuit is required to be installed, and further the arrangement of the terminals of the filters needs to be decided in consideration of their connection relation to connecting terminals on the printed circuit board. In this case, the designing of circuits is also significantly difficult.
Generally speaking, the arrangement of terminals of printed circuit boards for mounting antenna duplexers is pre-determined in many cases. Accordingly, the designing of the circuits of an antenna duplexer depends greatly on the pre-determined arrangement of terminals on a printed circuit board. That is, in the designing of the circuits of the antenna duplexer, the layout of the terminals of filter chips and the phase matching circuit must be designed taking into account the prevention of interference between signals and the pre-determined arrangement of the terminals on the printed circuit board.
Especially, the recent demand for reduction in size of terminal devices also requires duplexer packages to be smaller. In the duplexer packages, strip lines used as phase matching circuits, wires between signal terminals and wires to external circuits need to be arranged not to cross each other, or if they are required to cross each other for a desired size reduction, the duplexer packages should be constructed such that interference between signals is prevented in wire-crossing regions.
In one-piece duplexer packages in which phase matching circuits are mounted within the duplexer packages for reducing the size thereof, parasitic inductance is generated between layers, which is known to cause decline in attenuation outside a pass band.
FIGS. 28(a), 28(b) and 28(c) are graphical representations of frequency characteristics of SAW filters with changes of a parasitic inductance (L) in an antenna duplexer.
According to these graphical representations, the larger the parasitic inductance (L) is, the less the attenuation outside pass bands is.
Generally, when the phase matching circuit is integrated within a package, necessary circuits can be formed in a multi-layered structure, which lead to size reduction. However, this multi-layered structure causes an increase in the parasitic inductance. Accordingly, it is necessary to decrease the height of the duplexer package for improving the attenuation outside the pass band.
Further, if the distance between the strip line and signal terminals is decreased for size reducing of the duplexer package, capacity coupling tends to increase therebetween. This results in decline in the attenuation outside the pass band which is one of frequency characteristics. Accordingly, it is desired that the circuits are designed in consideration of the capacity coupling besides the decrease of the height of the duplexer package.
Also, in the case where two duplexers greatly different in their pass band frequencies are made into a single antenna duplexer, external circuits connected to the duplexers must be separately provided. On the other hand, in the case where two duplexers slightly different in their pass band frequencies are made into a single antenna duplexer, the construction of the antenna duplexer may be such that circuits are partially shared and switched by use of RF switches or the like for size reducing purpose. However, it is desirable that the number of RF switches be as small as possible from the viewpoint of desired size reduction and improvement of frequency characteristics.
Further, in the case where two duplexers greatly different in their pass band frequencies are made into a single antenna duplexer, SAW filters for composing the respective duplexers are produced under considerably different conditions and matching circuits added thereto have patterned lines of greatly different lengths. Accordingly, such differences must be taken into careful consideration when the layout of the duplexer package is designed.
FIG. 29 is a graphical representation showing a relationship between the velocity V of a surface acoustic wave (SAW) passing a SAW filter and a normalized thickness h/xcex of electrodes. Here, h represents the thickness of the electrodes and xcex represents the period of the electrodes. Generally the relationship of the center pass band frequency f0 of a filter, the SAW velocity V and the period xcex is represented by f0=V/xcex. Accordingly, a desired f0 is obtained by optimizing V and xcex. For example, as shown in FIG. 29, the normalized thickness h/xcex needs to be larger for reducing the SAW velocity V. However, there is a problem in that V changes greatly with respect to a change in h, and therefore, f0 becomes unstable.
In other words, in the case where two duplexers whose pass band frequencies are so different that the SAW velocities in the duplexers are significantly different are formed in a single package, comb-shaped electrodes of the SAW filters in the respective duplexers are greatly different in thickness, period and width. Therefore, it is also necessary to vary exposure conditions, etching conditions and other conditions in production of the SAW filters.
The present invention provides an antenna duplexer including two duplexer elements each including two surface acoustic wave filters having different center pass band frequencies; and connecting terminals for connecting the duplexer elements and external circuits, which are grouped into an antenna terminal group for connection to an external antenna, a receiving terminal group for connection to an external circuit and a transmitting terminal group for connection to an external circuit, wherein regions for disposing the antenna terminal group, the receiving terminal group and the transmitting terminal group are separated planarly.
With this construction, the antenna duplexer can be reduced in size with maintaining its required filter characteristics.